It is well known that open trough roof gutters fill with leaves and other debris causing impaired effectiveness of the gutter as a roof drainage system. Frequently, water accumulates in clogged gutters causing an overflow failure which can damage the building. If the gutters freeze, the expanding water can deform the gutter and may cause it to pull away from the building support. The water may also force its way back up under the shingles or roof covering, causing damage to the roof itself. Thus some form of gutter shield is desirable for separating (straining) debris from the water running off of a roof edge. Ideally, such a shield will not only allow, but encourage water to flow into the gutter while debris is separated and enabled to slide off the outer edge of the shielded gutter.
Some known gutter shields are formed of screen material (e.g., hardware cloth), or expanded metal screening in which a web of metal stock is slit and then drawn or expanded so as to laterally stretch open the slits to form openings for water and yet at the same time to shield the gutter from debris. Such systems, while somewhat effective in guarding against accumulation of larger debris (e.g., twigs and leaves) in the gutters, they have openings which are large enough to allow smaller items of debris (e.g., small seeds, “propeller” vanes on seed pods, evergreen “needles” and leaf fragments) to pass through either partly or entirely. If not removed, these materials accumulate and eventually clog the shield and/or the gutter.
Prior art gutter shields that, like the above-described screening, have a rather rough surface texture can become externally clogged because such arrangements allow debris to accumulate on the shield itself thereby blocking water's access to the gutter and rendering it ineffective. In such cases, water can well up about the accumulated debris and migrate under the edge of the roof and/or roof covering causing damage.
U.S. Pat. No. 6,073,398 (Williams; 2000) discloses a gutter cover with a planar back area (14) connected to a curved front portion (18) that leads water by capillary action into the covered gutter. It can be seen that debris (at least larger pieces) generally will not follow the curved portion and will instead wash off the outside edge of the covered gutter. Other examples of capillary action shields with gutter access holes beyond a curved portion include U.S. Pat. No. 5,251,410 (Carey; 1993) and U.S. Pat. No. 4,616,450 (Shouse; 1986).
A problem with designs such as Williams '398, Carey '410, and Shouse '450 is that in a hard rain, water flow is too great and a significant portion of the water will simply shoot outward beyond the outside edge of the covered gutter. In order to address this problem, gutter shields such as those disclosed in U.S. Pat. No. 5,640,809 (Iannelli; 1997) and U.S. Pat. No. 5,557,891 (Albracht; 1996) provide means for slowing down the flow of water. Iannelli '809 provides a substantially planar primary surface (20) that has longitudinal protuberances (35) and a rise (36); and Albracht '891 has a relatively wide horizontal portion (7).
There are also problems with gutter shields that are secured horizontally across the top opening of the gutter, or which have substantially planar or wide horizontal portions. Since debris may not be washed off of such horizontal portions, the weight of accumulated debris on the gutter, which bears the weight of the shield as well as the debris accumulated thereon, can cause the gutter or the shield to collapse and/or pull away from the fascia to which it is attached. Thus, the shield may create more problems than it solves. There is therefore a need for a gutter shield that is effective in preventing the accumulation of debris both in and on top of a gutter, and that allows the debris to fall away or be swept off of the shield by wind and rain.
The prior art contains a number of gutter shields that are sloped downward and outward and which have apertures through the downslope for separating water from debris. The optimum shape of the shield material around and leading into each aperture, and therefore the size, shape and location of an aperture, is the subject of much debate and is often a factor in distinguishing one shield from another. These shapes, etc. affect the water's flow rate, capillary action and sheeting, as well as the size/shape of debris that is filtered out and whether the debris will accumulate on the shield and/or clog its apertures.
Capillary action and sheeting are both effects of surface tension but may effectively work against each other. For example, capillary action results in water being “held” against a surface and “pulled” through an aperture toward which and/or through which the surface leads the water. In opposition to this, water may pass over an aperture if the water is held together by surface tension in a continuous “sheet”. Such a sheet must be effectively broken or perforated in order for any of the water to drain away into an aperture below the sheet. It is also possible for a sheet of water to form on the underside of a sloped surface, thereby forming a barrier to water flow down through the sheet from apertures above it.
U.S. Pat. No. 4,418,504 (Lassiter; 1983) discloses a sloped shield having apertures (19) that are positioned between an upstream arch followed by a trough. U.S. Pat. No. 6,016,631 (Lowrie, III; 2000) discloses a gutter device having a plurality of holes (31), preferably formed by creating a depression (31) in the downslope portion. U.S. Pat. No. 5,271,191 (Vahamaki; 1993) discloses a gutter shield having slotted (24) vanes (26) wherein the vanes are sloped downward at a vane angle (27) relative to the plane of the shield's stock material. U.S. Pat. No. 6,151,837 (Ealer, Sr.; 2000) discloses a perforated sheet gutter screen comprising a sheet metal member with a generally smooth top surface and a plurality of channels (54) and slots (56), wherein each channel extends downward and away from the top surface and has a lower end that defines a lower portion of the periphery of one of the slots, and has a concave profile such that an upper, leading edge of the channel is curved substantially along its full length.
In light of the abovedescribed problems and defects in the prior art, it is an object of the present invention to overcome these defects by providing a gutter shield that not only separates even small debris from rainwater, but furthermore resists accumulation of the debris on the gutter shield, and even further encourages the flow of water through the shield and into the shielded gutter even when water is flowing rapidly and tending to “sheet” above and/or below the shield.